Re: IBM test question

On Thu, 07 Feb 2008 17:27:53 +0100 Matthieu CASTET [off-list ref] wrote:

Hi Sébastien,

Sébastien Dugué wrote:

quoted

  Hello Matthieu,

On Thu, 07 Feb 2008 14:49:07 +0100 Matthieu CASTET [off-list ref] wrote:

quoted

hi,

I am trying to use some IBM rt test on arm.


I define atomic_add to
assert(i==1);
return ++(v->counter);

That's a bit ugly, but that should work for my need.

  That would be the poor man's atomic_inc() and not sure it really does
what you think it does ;). Just for the record, pre-armv6 cores have no support
for userland atomic operations (aside from swapping).

I can, if I use a kernel helper :) [1]

  Yep, but much slower.

BTW what should do the atomic_add.
On i386 it does the atomic add and return the value in memory before the 
add (Exchange and Add).

  Looking at the kernel and glibc, i386's atomic_add seems to be a void
function (unless I missed something).

On powerpc, it seems to do the atomic add and return the new value.

  Yes, both for kernel and glibc implementations.

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But I have a problem with the sched_latency test.
On my platform the thread creation is quite slow (25ms), so with the 
default value, I got a PERIOD MISSED.

  The IBM RT tests have been integrated into the LTP and I recently
sent some updates to those testcases. Notably one the patches did improve
the thread starting time. Other patches did touch this particular test too.

  Could you try the latest release (from LTP) and tell me if things
have improved for you.

Ok I will try them.

quoted

  Also, the PASS/FAIL criteria are quite arbitrary. They happen to be fine
for most recent PC-class hardware but surely not for embedded systems and
should be tuned according to your RT requirements.

Yes I saw that.

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Also my cpu is quite slow (compared to last intel core or powerpc). For 
example a sched_jitter run take 6s.

  Ouch! What's your CPU (core type, clock speed)?

Arm926 ~104.65 Mhz

  ARMv5 core then. You'll need the kernel helper then to be trully atomic.

  Sebastien.